(adapted for ngcgui from Chris Radek routine: P-hole.ngc)
(info: Probe hole, start from approx x,y center)

o<p-hole> sub
 #<maxradius> = #1 (=4)
    #<zsafe>  = #2 (=.1)
  #<feednorm> = #3 (=5)
  #<feedslow> = #4 (=0.05)
#<probediam>  = #5 (=.07874 probe diam)
  #<in_or_mm> = #6 (=21 in:20, mm:21)
    #<offset> = #7 (=0.025)
 #<finaldist> = #8 (=0.10)

G#<in_or_mm>      ; inch or mm
F#<feednorm>

G90
#<xstart>=#5420
#<ystart>=#5421
G91 G38.3 Z0.001 ; establish initial xcenter,ycenter with noerror probe move

;M110 ; clear axis ui notifications
      ; bug in interp_convert.cc prevents mulitple named params with debug,
      ; (debug, start x,y =#<xstart> #<ystart)
;(debug, start x,y =#5420,#5421)
(debug,Probe four times +x,-x,+y,-y at feednorm)
;(debug,Then probe again at feedslow)
;(debug,Press RESUME to begin)
M0
#<xcenter>=#5061
#<ycenter>=#5062

G91 G38.2 X#<maxradius>             ; incremental +x probe
#<xplus>=#5061
G90 G0 X#<xcenter>                  ; absolute move to xcenter
G91 G38.2 X[0-#<maxradius>]         ; incremental -x probe
#<xminus>=#5061
#<xcenter>=[[#<xplus>+#<xminus>]/2] ; new xcenter
G90 G0 X#<xcenter>                  ; absolute move to xcenter

G91 G38.2 Y#<maxradius>
#<yplus>=#5062
G90 G0 Y#<ycenter>
G91 G38.2 Y[0-#<maxradius>]
#<yminus>=#5062
#<ycenter>=[[#<yplus>+#<yminus>]/2]
G90 G0 Y#<ycenter>

F#<feedslow>

G90 G0 X[#<xplus>-#<offset>]
G91 G38.2 X#<finaldist>
#<xplus>=#5061
G90 G0 X[#<xminus>+#<offset>]
G91 G38.2 X-#<finaldist>
#<xminus>=#5061
#<xcenter>=[[#<xplus>+#<xminus>]/2]
G90 G0 X#<xcenter>

G90 G0 Y[#<yplus>-#<offset>]
G91 G38.2 Y#<finaldist>
#<yplus>=#5062
G90 G0 Y[#<yminus>+#<offset>]
G91 G38.2 Y-#<finaldist>
#<yminus>=#5062
#<ycenter>=[[#<yplus>+#<yminus>]/2]
G90 G0 Y#<ycenter>

#<xdia>  = [#<xplus>-#<xminus>+#<probediam>]
#<ydia>  = [#<yplus>-#<yminus>+#<probediam>]
#<dia>   = [[#<xdia>+#<ydia>]/2]
#<angle> = [atan[#<ycenter>]/[#<xcenter>]]
#<dist>  = [sqrt[[#<xcenter>*#<xcenter>]+[#<ycenter>*#<ycenter>]]]

G0 Z#<zsafe>
(debug,Xdia=#<xdia> Ydia=#<ydia> Dia=#<dia> Ang=#<angle> Dist=#<dist>)
(debug,Xcenter=#<xcenter>  Ycenter=#<ycenter> Dia=#<dia>)

o<p-hole> endsub